Cured silicone powders are used as additives, for example, to cosmetics, paints, inks, thermosetting organic resins, and thermoplastic organic resins. Cured silicone powders are particularly well suited for use as internal stress relaxers for thermosetting organic resins and as surface lubricants for organic resin films.
Cured silicone powders can be produced, for example, by grinding silicone rubber, by curing a liquid silicone rubber composition while spray drying (see Japanese Patent Application Laid Open Number [hereinafter referred to as “Kokai”] S59-68333), and by curing a liquid silicone rubber composition while it is dispersed in water (see Kokai S62-243621, Kokai S63-77942, Kokai S63-202658, and Kokai S64-70558).
However, the cured silicone powders afforded by these methods have a strong tendency to aggregate and, as a result, have a poor flowability. Further, they have poor dispersibility in aqueous coating materials, cosmetic materials, or similar aqueous compositions. If a cured silicone powder is non-uniformly dispersed in an aqueous composition and forms aggregates, it is difficult to provide uniform surface dullness, when used in coating materials, and impairs tactile feeling, when used in cosmetic products.
Composite cured silicone powders with adherence of the inorganic fine powder to the surfaces of the composite powders and with improved flowability have been proposed (see Kokai H4-348143, Kokai H5-179144, and Kokai H7-102075). These composite cured silicone powders, however, exhibit poor hydrophilicity, and thus impart poor hydrophilicity to aqueous compositions in those applications where they are blended with such compositions.
It has also been proposed (see Kokai H7-196815) to coat the surfaces of silicone rubber powder particles with a polyorganosilsesquioxane resin, or to coat the surfaces of particles of oil-containing silicone powder with an organic fine powder (see Kokai H9-208709).
However, the aforementioned composite cured silicone powders still had insufficient hydrophilicity and dispersibility in aqueous compositions.